Interferons are cytokines secreted by cells (esp. white blood cells) in response to viral infections. Interferons can bind to receptors on noninfected neighboring cells and induce the cells to produce proteins that increase their resistance to viral infections. The proteins produced interfere with the transcription of the viral genetic material, as well as increase the speed and strength of the immune response through the expression of class I MHC molecules.
Interferon alpha (IFN-α) is a member of Type I interferons, which mediate the early innate immune response to viral infections. This family has been tested for both the modulation of aberrant immunological responses and as a therapy for a variety of diseases such as AIDS and hepatitis.
The use of IFN-α as a therapeutic is compromised by its limited in vivo half-life in the body. Short in vivo half-life means that therapeutic glycopeptides must be administered frequently in high dosages, which ultimately translate to higher health care costs than might be necessary if a more efficient method for making longer lasting, more effective glycoprotein therapeutics were available.
One solution to the problem of providing cost effective glycopeptide therapeutics has been to provide peptides with longer in vivo half lives. For example, glycopeptide therapeutics with improved pharmacokinetic properties have been produced by attaching synthetic polymers to the peptide backbone. An exemplary polymer that has been conjugated to peptides is poly(ethylene glycol) (“PEG”). The use of PEG to derivatize peptide therapeutics has been demonstrated to reduce the immunogenicity of the peptides. For example, U.S. Pat. No. 4,179,337 (Davis et al.) discloses non-immunogenic polypeptides such as enzymes and peptide hormones coupled to polyethylene glycol (PEG) or polypropylene glycol. In addition to reduced immunogenicity, the clearance time in circulation is prolonged due to the increased size of the PEG-conjugate of the polypeptides in question.
The principal mode of attachment of PEG, and its derivatives, to peptides is a non-specific bonding through a peptide amino acid residue (see e.g., U.S. Pat. Nos. 4,088,538 4,496,689, 4,414,147, 4,055,635, and PCT WO 87/00056). Another mode of attaching PEG to peptides is through the non-specific oxidation of glycosyl residues on a glycopeptide (see e.g., WO 94/05332).
In these non-specific methods, poly(ethyleneglycol) is added in a random, non-specific manner to reactive residues on a peptide backbone. Of course, random addition of PEG molecules has its drawbacks, including a lack of homogeneity of the final product, and the possibility for reduction in the biological or enzymatic activity of the peptide. Therefore, for the production of therapeutic peptides, a derivitization strategy that results in the formation of a specifically labeled, readily characterizable, essentially homogeneous product is superior. Such methods have been developed.
Specifically labeled, homogeneous peptide therapeutics can be produced in vitro through the action of enzymes. Unlike the typical non-specific methods for attaching a synthetic polymer or other label to a peptide, enzyme-based syntheses have the advantages of regioselectivity and stereoselectivity. Two principal classes of enzymes for use in the synthesis of labeled peptides are glycosyltransferases (e.g., sialyltransferases, oligosaccharyltransferases, N-acetylglucosaminyltransferases), and glycosidases. These enzymes can be used for the specific attachment of sugars which can be subsequently modified to include a therapeutic moiety. Alternatively, glycosyltransferases and modified glycosidases can be used to directly transfer modified sugars to a peptide backbone (see e.g., U.S. Pat. No. 6,399,336, and U.S. Patent Application Publications 20030040037, 20040132640, 20040137557, 20040126838, and 20040142856, each of which are incorporated by reference herein). Methods combining both chemical and enzymatic synthetic elements are also known (see e.g., Yamamoto et al. Carbohydr. Res. 305: 415-422 (1998) and U.S. Patent Application Publication 20040137557 which is incorporated herein by reference).
Interferon α (IFN-α) is an extremely valuable therapeutic peptide. Although commercially available forms of IFN-α are in use today, these peptides can be improved by modifications that enhance the pharmacokinetics of the resulting isolated glycoprotein product. Thus, there remains a need in the art for compositions including IFN-α with improved effectiveness and pharmacokinetics. Furthermore, to be effective for the largest number of individuals, it must be possible to produce, on an industrial scale, a composition including IFN-α with improved therapeutic pharmacokinetics that has a predictable, essentially homogeneous, structure which can be readily reproduced over and over again.
The present invention fulfills these, and other, needs.